Heretofore, one of such techniques has been known as an evaporated fuel treatment apparatus disclosed in for example JP 2007-303346A. This apparatus is designed for use in engines of a hybrid vehicle (HV) and a vehicle equipped with a continuously variable transmission (CVT), which are recently actively developed.
In general, an evaporated fuel treatment apparatus is configured to purge evaporated fuel collected or trapped in a canister by use of a negative pressure generated in an intake passage so that the evaporated fuel is fed into the intake passage. Accordingly, this apparatus has a problem that could not sufficiently purge the evaporated fuel to the intake passage when the negative pressure in the intake passage decreases. The engines of the HV vehicle and the CVT-equipped vehicle are usually subjected to air-fuel ratio control that more often utilizes fuel-saving, low-rotation and high-load regions. Accordingly a throttle valve is frequently brought into a widely open state over all the operations, resulting in that a negative pressure may be less apt to occur in the intake passage. In particular, during normal operation of the engine, that is, during steady operation or accelerated operation, the negative pressure is less likely to occur in the intake passage. In the engines of the HV vehicle and the CVT-equipped vehicle, it is hard to make effective use of the evaporated fuel treatment apparatus by utilization of the negative pressure in the intake passage.
Accordingly, the evaporated fuel treatment apparatus disclosed in JP 2007-303346A includes an ejector in the intake passage to generate a larger negative pressure than the negative pressure in the intake passage. The ejector is placed in a bypass passage provided for the intake passage. To purge the evaporated fuel collected in the canister to the intake passage, a second end of a first path whose first end is connected to the canister is connected to the ejector. A first end of a second path is connected to some midpoint of the first path through a three-way valve. A second end of the second path is connected to the intake passage. The three-way valve is switched according to an operating state of the engine to purge the evaporated fuel collected in the canister from the first path to the intake passage via the three-way valve and the second path or purge more evaporated fuel from the first path to the intake passage via the ejector.